Header Injector – Custom HTTP Headers

Modify and inject custom HTTP request headers globally, per domain, or per path. For developers, API testing, and debugging.

Header Injector – Custom HTTP Headers lets you add, modify, or override HTTP request headers directly in Chrome — no proxy setup, no code changes. Whether you're testing APIs, debugging authentication, or simulating different client environments, Header Injector gives you full control over outgoing request headers from a clean side panel. ✨ KEY FEATURES 🌐 Global headers Apply custom headers to every request in your browser. Perfect for setting Authorization tokens, API keys, or custom flags across all sites. 🏷️ Per-domain rules Target specific websites with domain-based rules. Enter a hostname like example.com — subdomains like api.example.com are included automatically. 📁 Path matching Optionally narrow rules to specific URL paths. Use wildcards to match entire API routes: • /api** → everything under /api • /api/users → one exact endpoint 🔘 Toggle on/off Enable or disable global rules and individual domain groups without losing your configuration. 💾 Persistent settings Your header rules are saved locally and restored automatically when you reopen Chrome. 🎯 USE CASES • API testing — inject Bearer tokens, API keys, or custom auth headers • Feature flags — send X-Feature-Enabled or A/B test headers • Local development — simulate production headers on localhost • Debugging — reproduce client-specific request behavior • QA & staging — switch environments without changing app code 🔒 PRIVACY All configuration is stored locally on your device. Header Injector does not collect, transmit, or share any data with external servers. Your headers and rules never leave your browser. 📖 HOW TO USE 1. Click the Header Injector icon to open the side panel 2. Add headers under "All requests" for global rules, or "Specific domain" for targeted rules 3. Toggle rules on or off as needed 4. Reload the page — your headers are applied instantly Built for developers who need a simple, reliable way to customize HTTP request headers.